The role of hypothalamic biogenic amines in the "gonadostat theory of puberty" is to be examined by: 1) characterizing the alterations that occur in hypothalamic biogenic amine content and turnover during normal sexual maturation in male and female rats; 2) determine the effect of gonadal secretions on these parameters by repeating biogenic amine measuremnts in castrate animals of similar ages; and 3) testing the hypothesis that changing sensitivity of the hypothalamic-pituitary axis to the negative feedback effects of gonadal steroids is mediated through changes in hypothalamic neurotransmitter metabolism. Intact an castrate male and female rats will be sacrificed at various ages during sexual maturation. Other groups of male and female rats are to be castrated and implanted with silastic capsules containing four increasing doses of testosterone or estradiol respectively. After six days these animals will be sacrificed. Serum will be obtained from all animals for the determination of LH, FSH, estradiol and/or testosterone (by RIA). Brains will be removed for measurement of norepinephrine and dopamine content (by I125 RIA), serotonin content (by radioenzymatic assay) and NE turnover (by the alumina extraction method of intraventricularly administered H3NE). The biogenic amine measurement will be performed in four subdivisions of the hypothalamus: ventral anterior hypothalamus, dorsal anterior hypothalamus, medial basal hypothalamus and residual hypothalamus. By this approach, the complex relationships between gonodal steroids, biogenic amine metabolism in specific hypothalamic areas and pituitary gonadotropin secretion during sexual maturation can be defined and insight gained into the role of these systems in the process of puberty.